To mix different liquids or a liquid with a gas in a controlled manner, porous membranes are often used as a barrier between the materials. A unidirectional pressure gradient from one side of the membrane to the other often determines the direction of flow of the materials through the membrane. The properties of the membrane itself also affect the flow of materials from one side of the membrane to the other.
Referring to FIG. 2, a prior art humidifier is shown generally as 30. The prior art humidifier includes a container 32 having a hydrophilic membrane 34 that divides container 30 into two chambers, 36 and 38. A fluid, such as water, is introduced into chamber 36 via an inlet 40 and exits the chamber via outlet 42. A second fluid or gas, such as air, is introduced into chamber 38 via a second inlet 46 and exits the chamber via a second outlet 44. The fluids may flow in either co-current or counter-current directions.
Membrane 34 has micro-pores that fill with water due to the hydrophilic nature of the material. To prevent water from entering the air chamber 38, chamber 38 must be maintained at a constant higher pressure than chamber 36. If the pressure gradient is not maintained, water droplets can migrate into the air chamber and be dispersed by the flow of air. This can be particularly onerous when the humidifier is used in a respiratory track therapy application in which water droplets can be carried undesirably into a patient's lungs.
Referring to FIG. 3, another prior art humidifier is shown generally as 50. This prior art humidifier includes a container 52 in which a hydrophobic membrane 54 is disposed. Membrane 54 divides container 52 into two chambers, 56 and 58. A fluid, such as water, is introduced into chamber 56 via an inlet 60 and exits the chamber via an outlet 62. A second fluid or gas, such as air, is introduced into chamber 58 via a second inlet 64 and exits via a second outlet 66. Due to the hydrophobic properties of membrane 54, the membrane's micro-pores are filled with air. To prevent air from leaking into water chamber 56, chamber 56 must be maintained at a constant higher pressure than chamber 58. Due to the limited characteristics of the membranes, pressure gradients must be constantly and precisely monitored and controlled to prevent unwanted migration of one fluid into the other.
Contemporary humidifiers used in respiratory track therapy applications are based on hydrophilic hollow fiber cartridges that employ sensitive pressure control to prevent water droplets from entering into the air stream and into the patient. A persistent problem with water droplet migration occurs when the units are idle. What is needed and desired is a humidifier that prevents water droplet migration independent of the apparatus' activity status and independent of pressure gradients. These and other objects of the invention will become apparent from a reading of the following summary and detailed description of the invention.